The present invention relates to apparatus for drying cavities in microtitration filter trays and filters received therein, further to a system incorporating such apparatus, and to a method to dry microtitration filter trays and filters received therein.
Apparatus, systems and methods of this kind are used in particular when processing liquid test samples, mostly contained in buffers in microtitration filter trays.
Conventional microtitration filter trays are fitted, for instance, with 96 cavities each presenting an upper and a lower aperture, a filter being configured in the region of the lower aperture and covering its cross-section.
The samples are pipetted into the individual microtitration filter tray cavities and then are aspirated by vacuum filtration through the filters and thereby are separated into components. If the components absorbed in the filters are found to be significant, then in most instances, following test sample filtration, a washing solution will be applied several times into the cavities and will be aspirated through the filters. Next, an elution buffer is used to remove the significant components of the liquid test samples from the filter. Accordingly, conventional processing entails moving different liquids sequentially through the filters configured in the microtitration filter tray cavities.
A problem is encountered, in particular, when using buffering or washing solutions containing an alcohol or other organic solvents (isopropanol) that are miscible with water on account of the solvents fixating in the filter capillaries and possibly then interfering with subsequent reactions. Also, residues of the solvent that was used remain as drops on the cavity side walls, especially at the exit side underneath the filters.
As a result, between filtration stages, especially when alcohol-containing buffers or washing solutions are employed, the particular residual liquid ought to be removed each time. This desideratum also applies to the drops on that cavity wall. Consequently, a drying procedure usually is used in the state of the art.
A number of methods to dry cavities and the filters of a microtitration filter tray are known. The simplest one, which however entails prohibitively time-consuming process steps, would be to let the microtitration filter tray stand a long enough time to allow the residual liquid, in particular a substantially volatile alcohol, to evaporate into the ambient air.
Evaporation might be accelerated by heating the microtitration filter tray. Such a design is illustratively shown in the US patent document 2004/0033619 A1 and in the European patent document EP 1257363 B1. It was noted however that relatively high temperatures are needed to assure good drying of the cavities and filters. Such high temperatures, in turn, may damage the microtitration filter tray and also be injurious to the samples.
It is further known to dab off the cavities and filters with absorbent paper. While dabbing may be automated and in fact is very effective on the drops remaining on the cavity walls, on the other hand it only removes the residual liquid on or near the filter surface. More deeply imbedded residual liquid cannot be removed in this manner.
Again, the residual liquid in the cavities and filters might be eliminated by centrifuging. This approach entails the drawback of having to remove the microtitration filter tray out of the vacuum chamber and place it in a centrifuge. Such an additional operational step is undesirable, especially as regards method automation.
It is further known from the German patent DE 101 44 225 C1 to apply an airflow through the upper cavity apertures to the filters. However, this method is fairly time-consuming.